1. Field of the Invention
The invention relates to a liquid crystal display (LCD) device and more particularly, to a manufacturing method of embossing patterns and a reflective liquid crystal display device including the same.
2. Discussion of the Related Art
liquid crystal display (LCD) devices have been spotlighted as a next generation display device having high value added because of their low power consumption and good portability.
Optical anisotropy and the polarization characteristics of a liquid crystal material constitute the basis for driving a LCD device. In general, an LCD device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the two substrates includes an electrode, and the electrodes of each substrate also face each other. Voltage applied to each electrode induces an electric field between the electrodes. Alignment of the liquid crystal molecules is changed by varying the intensity or direction of the electric field. The LCD device displays a picture by varying transmittance of the light according to the arrangement (or rearrangement) of the liquid crystal molecules.
An active matrix liquid crystal display (AMLCD) device, which includes thin film transistors as a switching device for a plurality of pixels, has found wide used due to its high resolution and fast moving images.
A related art LCD device will be described hereafter in detail with reference to figures.
FIG. 1 shows a schematic solid view illustrating a related art LCD device. In this LCD device, upper and lower substrates 10 and 30 are spaced apart from and facing each other, and a liquid crystal layer 50 is interposed between the upper substrate 10 and the lower substrate 30.
At least one gate line 32 and at least one data line 34 are formed over the inner surface of the lower substrate 30 (i.e., the side facing the upper substrate 10). The gate line 32 and the data line 34 cross each other to define a pixel region P. A thin film transistor T serves as a switching element, and is formed at the crossing of the gate line 32 and the data line 34. Although not shown in detail in FIG. 1, the thin film transistor T includes a gate electrode, a source electrode, a drain electrode, and an active layer. An array of such thin film transistors T is arranged in a matrix form corresponding to crossings of gate and data lines. A pixel electrode 46, which is connected to the thin film transistor T, is formed in the pixel region P.
The upper substrate 10 includes a color filter layer 12 and a common electrode 16 respectively formed on the inside (i.e., the side facing the lower substrate 30). Although not shown in detail in the figure, the color filter layer 12 includes three sub-color filters of red (R), green (G), and blue (B) transmitting light in a specific wavelength range, and a black matrix blocks light in an area where liquid crystal molecules are not controlled. The black matrix is disposed between the sub-color filters. Each sub-color filter of the color filter layer 12 corresponds to the pixel electrode 46 at the pixel region P.
Upper and lower polarizers 52 and 54, each of which may be a linear polarizer that transmits only linearly polarized light parallel to its light transmission axis, are arranged over outer surfaces of the upper and lower substrates 10 and 30, respectively. Additionally, a backlight disposed over the outer surface of the lower polarizer 54 functions as a light source.
Generally, during a selecting period when a gate signal having an ON state is applied to the gate line 32, voltage applied to the gate electrode (which is connected to the gate line 32) is higher than voltage of the data line 34. Thus, the resistance of a channel between the source and drain electrodes is lowered. Accordingly, the pixel electrode 46 applies the voltage of the data line 34 to the liquid crystal layer 50.
During a non-selecting period, voltage applied to the gate electrode connected to the gate line 32 is lower than voltage of the data line 34. Therefore, the source and drain electrodes are electrically cut, and charges accumulated in the liquid crystal layer 50 are preserved.
In general, a transmissive LCD device utilizes a backlight as an additional light source. However, the backlight of the transmissive LCD device consumes over ⅔ of the total power of the LCD device. Recent developments include a reflective or transflective LCD device, which uses an ambient outer light to reduce the consumption of power or battery drain. A reflective LCD device does not include a backlight.
A reflector having embossing patterns may be used in the reflective or transflective LCD device to increase the amount of light reflected toward a front side by changing local reflective angles.
FIG. 2 illustrates a cross-sectional view of a related art reflective LCD device including embossing patterns. In FIG. 2, a thin film transistor T is formed on a first substrate 60, where a pixel region P is defined as a minimum unit for displaying images. The thin film transistor T includes a gate electrode 64, a semiconductor layer 66, a source electrode 68 and a drain electrode 70. Embossing patterns 72 are formed in the pixel region P on the first substrate 60 including the thin film transistor T. The embossing patterns 72 are spaced apart from each other. The embossing patterns 72 serve as a kind of seed. A passivation layer 76 covers the thin film transistor T and the embossing patterns 72. The passivation layer 76 includes a drain contact hole 74 that exposes a part of the drain electrode 70. The passivation layer 76 has a thickness such that a surface of the passivation layer 76 also has an embossing structure due to the embossing patterns 72.
A reflective electrode 78 is formed on the passivation layer 76 and connects to the drain electrode 70 through the drain contact hole 74. The reflective electrode 78 has a surface of an embossing structure caused by the embossing patterns 72 and the passivation layer 76. The reflective electrode 78 acts as a pixel electrode.
A second substrate 80 is spaced apart from and faces into the first substrate 60. A black matrix 82 is formed on an inner surface of the second substrate 80. The black matrix 82 corresponds to the thin film transistor T and a data line 69, which is connected to the source electrode 68. A color filter layer 84 is formed on the black matrix 82, and a common electrode 86 is formed on the color filter layer 84.
FIGS. 3A to 3F illustrate a manufacturing process of related art embossing patterns.
In FIG. 3A, coating a photosensitive organic material forms a first insulating layer 91 on a substrate 90. For example, an acrylic-based photoresist may be used as the photosensitive organic material.
FIG. 3B shows the first insulating layer 91 being selectively exposed to light using a mask 99, which includes opening portions 99a and blocking portions 99b. Here, the photosensitive organic material may be a positive type, in which a portion that has been exposed to light is removed.
FIG. 3C shows convex patterns 92 being formed by developing the exposed first insulating layer 91 of FIG. 3B using a developer.
FIG. 3D shows embossing patterns 93 that are formed by repeatedly melting and baking the convex patterns 92. The embossing patterns 93 function as a seed of a micro reflector.
FIG. 3E shows a second insulating layer 94 covering the embossing patterns 93 that is coated on the substrate 90 in order to widen angles of reflection at the embossing patterns 93 by controlling inclined angles of the embossing patterns 93. The second insulating layer 94 may be selected from the same material as the first insulating layer 91, for example, acrylic-based photoresist. The second insulating layer 94 has sufficient thickness to ensure that a surface of the second insulating layer 94 has an embossing structure due to the embossing patterns 93.
FIG. 3F shows a reflecting layer 96 that is formed on the second insulating layer 94, and the reflecting layer 96 forms by using a metal material that reflects light well. The reflecting layer 96 also has an embossing structure. The metal material for the reflecting layer 96 may be selected from aluminum (Al), silver (Ag), and so on.
Incident light from the outside is reflected toward the front viewing side by the reflecting layer of the embossing structure.
However, manufacturing the reflecting layer having the embossing structure requires a photolithographic process that includes steps for exposing and developing the first insulating layer. In addition, the second passivation layer is also formed. Therefore, the manufacturing process is complicated, and the manufacturing time lengthens and is accompanied by lower processing efficiencies.